- Originally standing for RAdio Direction And Range.
Mid-20th century. English.
A common enough device on land and at sea nowadays. Shipborne radars had a breakthrough in 1940 when a magnetron capable of producing short wavelengths under 10 cm was developed by the British. By 1943, radar sets were capable of wavelengths of 1.9 cm which could detect a submerged U-boat‘s periscope. Radars work when a transmitter sends out radio waves in pulses which are reflected back to a receiver. Since radio waves travel at the speed of light, the known speed and the time taken for these ‘echoes’ to return can then be measured which gives the distance to an object.
Kemp, P. (1994). The Oxford Companion to Ships and the Sea. Oxford University Press.
Rogers, J.G. (1985). Origins of Sea Terms. Mystic Seaport.